1. Field of the Invention
The invention relates to a semiconductor structure and a manufacturing method of the same. More particularly, the invention relates to a bump structure and a manufacturing method thereof.
2. Description of Related Art
In a fabricating process of a semiconductor, a conductive bump is required to be formed on each pad of the wafer structure that will serve as a flip-chip package, and the conductive bump that transmits electric signals includes a solder bump, a gold bump, a copper bump, a conductive polymer bump, a polymer bump, and so on. When an electric field is applied to the bumps, stress resulting from electro-migration is generated. Namely, when the bumps made of metal materials conduct electricity, metallic atoms of the bumps migrate along the grain boundary of the material and move toward the current-flow direction, which leads to the reduction of the sectional area of the bumps and finally causes an open circuit. Accordingly, it is necessary to form the so-called under bump metallurgic (UBM) layer between the bumps and pads, so as to enhance the bonding strength between the bumps and the pads and prevent the electro-migration phenomenon.
However, since the conventional UBM layer is merely configured below the bumps, an under cut effect is likely to be generated when there are cracks between the UBM layer and the bumps or between the UBM layer and the passivation layer that is located above the pads. Moreover, the bumps must have certain height, such that the bumps can be electrically connected to a circuit board or any other carrier. Hence, given the gold bumps are applied, the higher the gold bumps, the more the manufacturing costs. By contrast, when the gold bumps are replaced by the copper bumps, the manufacturing costs can be reduced. Nevertheless, copper is apt to be oxidized, which may give rise to the reduction of the bonding reliability between the bumps and the UBM layer.